The instant invention relates to automatic testing of the monitoring function of an electronic sensor at a work station of a textile machine in which spun yarn is wound up on cross-wound bobbins. Such textile machines may be ring spinning machines, rotor spinning machines, winding machines or twisting machines.
Electronic sensors with different monitoring/functions are used at each work station of the various textile machines. These monitoring functions may consist of:
Monitoring the presence of the yarn produced PA1 Monitoring the limit value for reaching a desired bobbin diameter in a cross-wound bobbin. PA1 the work station to stop its activity in case of a yarn breakage, PA1 the work station to be stopped when a desired bobbin diameter has been attained and a bobbin replacement is to be initiated. PA1 "Yarn present" or PA1 "No yarn present"
The electronic sensors function without physical contact with the monitored object. The work stations of a textile machine define a yarn course. The yarn course goes to a winding station where a cross-wound bobbin is produced. The different work stations of the textile machine are equipped with identical sensors. The sensors used to monitor the presence of the produced yarn monitor the state of yarn presence or yarn absence and form a signal for the corresponding state.
The sensor monitoring the limit values for an attained bobbin diameter detects the state when the bobbin diameter is still too small and the state when the bobbin diameter has attained the predetermined limit value. The sensor emits a corresponding signal for each state. It is characteristic for both sensors to work with binary signals. This indication of state is achieved electronically through a logical level display.
The sensors of a work station transmit their signals to a control unit. The control unit receives and processes the signals of the sensors of several work stations, i.e. the stations in one machine section. If the sensors detect a state (as described above), they signal it by means of a binary signal to the control unit of the machine section. On the basis of this signal the machine section may cause:
This will be explained in greater detail below through the example of a sensor used to monitor the presence of the produced yarn. A sensor of this type is a yarn monitoring system. The yarn monitoring system must monitor the course of the yarn and/or the yarn quality in any case. The yarn monitoring system recognizes two logical levels in monitoring the course of the yarn:
Developments in electronics have replaced the mechanical yarn monitor as the latter was often subject to damage due to operator errors. With the electronic yarn monitoring system it was possible to integrate yarn quality monitoring in addition to the function consisting of monitoring the presence of the yarn into one single component.
Quality monitoring necessarily requires the yarn-presence monitoring function, i.e. if no presence of yarn is signalled, the quality monitoring feature need not operate. In a yarn monitoring system incorporating both functions, it is possible to draw conclusions concerning quality monitoring by testing the yarn-presence monitoring function. Since the quality monitoring function depends primarily on the function of the yarn-presence monitor, an indication concerning the function of the yarn-presence monitor is sufficient in order to finally evaluate the function of the yarn monitoring system. Testing the yarn monitoring system is understood to mean testing its yarn-presence monitoring function. Spinning machines having no yarn monitoring system are however provided with at least a yarn-presence monitor and can also be included in the following discussion. The following discussion similarly applies also to an electronic sensor used to monitor the limit value of the bobbin diameter of the cross-wound bobbin to be produced.
It may occur that the function of the electronic yarn monitoring system is interrupted. Such interruptions can be provoked in electronic yarn monitoring systems operating on capacitive as well as according to optical principles.
Dirt may cause an erroneous level to be formed, i.e. the presence of a yarn may be signalled even though none is present, or is not even recognized as such. This problem may occur as a result of electrostatic supercharging of the yarn monitoring system. Such electrostatic supercharges may be produced due to the friction caused by the running yarn between yarn and yarn monitoring system, for example at the end points of the traversing movement. This causes flying fibers to be deposited and to be spread in the running direction of the yarn so that they may simulate the course of a yarn. This may also cause an erroneous level indication. Defects in the electronic system of the yarn monitoring system due to age, temperature influences, etc. are also possible.
An interference with the functions of the yarn monitoring system may have serious consequences, e.g. damage to or destruction of operating elements. The possibility of controlling the functioning of the yarn monitoring system is therefore needed.
The yarn monitoring system at the spinning station of an open-end spinning machine controls fiber feed after piecing as a function of the operating conditions which occur (i.e. depending on whether the piecing process has been successful or not). If fiber feed is started up as a result of an erroneous level indication of the yarn monitoring system, even though no yarn draw-off takes place, this leads to new production stoppages and to damage inflicted upon the spinning elements of the spinning station.
DE-OS 39 00 088 describes the monitoring of the functions of electronic yarn-presence monitors, whereby the latter detect yarn breakage. The known solution is based on the principle that a verification is carried out before each bobbin replacement to ascertain that all those yarn-presence monitors having signalled no yarn breakage before bobbin replacement do signal yarn breakage during the bobbin replacement. A yarn monitor which did not signal any yarn breakage before the bobbin replacement must signal a yarn breakage during bobbin replacement, otherwise it is considered to be defective. The known system merely checks whether the sensor (yarn-presence monitor) indicates a change in the output signal (change of the logical level). It is a disadvantage that even after a level change it is impossible to recognize whether the indicated state (level) is correct, so that the functional test does not provide sufficient certainty.